This invention relates to a gas turbine.
More particularly, the present invention relates to a gas turbine with a compressor area which has a rotor shaft to carry the rotor blades and a casing to carry stator vanes, with related rotor blades and stator vanes forming an axial clearance space between one another. Within the framework of the present invention the term compressor area shall be read to apply to the portion of either a fan or a compressor.
The aerodynamic loading of fans and compressors of aero engines and stationary gas turbines is limited by the requirement of sufficient flow stability. The loading of the individual compressor stages may, however, be increased by taking special measures against flow stall or surge.
The present invention relates to the design of the walls of both the rotor shaft and the casing in the compressor area specified.
The present invention further relates to compressor areas of the axial, semi-axial or radial types.
In accordance with the present invention, one or more compressor areas are provided, each comprising a rotor-stator configuration or a stator-rotor configuration. The rotor here is formed by a number of rotor blades attached to a rotor shaft and the stator is formed by a number of stator vanes attached to a casing. In this respect, both the rotor and the stator correspond to the designs known from the state of the art.
In accordance with the present invention, the stator vanes may also have the form of intake guide vanes.
The characteristics of the pressure ratio and of the mass flow shown by a partial or complete compressor at constant rotational speed have a negative gradient throughout a larger flow-value range. When mass flow is reduced, the characteristics become more and more flat and the sign of the gradient changes from negative to positive. This is normally the point at which the compressor becomes unstable and enters into a state of rotary flow stall or surge, respectively. These two operating states delimit the operating range of the compressor and may result in the compressor or the entire gas turbine being damaged.
Various solutions are proposed in the state of the art to avoid the above disadvantages:
A first measure is to produce slots, grooves, bores or ducts in the casing wall which are situated partly or wholly in the area of the aerofoil ends of the rotor blades.
A further measure is to produce slots, grooves, bores or ducts in the wall of the rotor shaft which are situated wholly or partly in the area of the stator vanes.
As a third measure, it was proposed to provide means for the detachment of the casing-near flow before or within the path of movement of the rotor blades, these means being known as separators.
The measures known from the state of the art are provided on an essential portion of the circle of movement or the area of movement of the rotor blades or the stator vanes, respectively. Accordingly, they are provided either above the rotor in the area of the rotor blade ends or below the stator in the area of the stator vane ends. These arrangements cause an unsteady disturbance of the flow in the area of the radial gaps of the rotor blades or the stator vanes, respectively. This leads to a considerable efficiency loss. Furthermore, mechanical problems during manufacturing as well as vibration-related problems will be encountered. In summary, all of the known measures are extremely cost-intensive to manufacture.